Bicycle damper

ABSTRACT

A damper for a bicycle, having a primary unit including a damper tube, a piston rod that supports a main piston, a reservoir tube that is outside of the compression chamber of the primary tube, and an inertial valve within the reservoir tube. The damper also includes a flow path connecting the reservoir fluid chamber and the compression chamber of the primary tube. The damper also may have a damping valve in the reservoir tube. When the inertia valve is open, the damping valve opens before flow through the inertia valve is maximized. The main piston and the damper tube at least partially define a compression chamber and a rebound chamber. The main piston is movable within the damper chamber of the primary unit. The reservoir tube includes a reservoir fluid chamber. The inertial valve is responsive to terrain-induced forces and not responsive to rider-induced forces when the shock absorber is assembled to the bicycle.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference and made a part of thepresent disclosure.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention generally relates to vehicle suspension systems.More specifically, the present invention relates to an improved shockabsorber system to be incorporated into the suspension system of abicycle.

Description of the Related Art

Bicycles intended for off-road use, i.e., mountain bikes, commonlyinclude a suspension assembly operably positioned between the rear wheelof the bicycle and the frame of the bicycle. The suspension assemblytypically includes a shock absorber configured to absorb forces impartedto the bicycle by bumps or other irregularities of the surface on whichthe bicycle is being ridden. However, an undesirable consequence ofincorporating a suspension assembly in a bicycle is the tendency for theshock absorber to absorb a portion of the power output of a rider of thebicycle. In some instances, i.e. when the rider is standing, theproportion of power absorbed by the shock absorber may be substantialand may drastically reduce the efficiency of the bicycle.

Vehicle shock absorbers utilize inertia valves to sense rapidaccelerations generated from a particular part of the vehicle. Inertiavalves are also used to change the rate of damping in the shock absorberdepending on the magnitude of the acceleration. As an example, theinertia valve assembly may be arranged to adjust the damping of the rearshock in accordance with accelerations that are generated by the body ofthe vehicle differently than it would adjust the damping of the rearshock for accelerations that are generated by the rear wheel of thevehicle.

One example of the type of shock absorber that utilizes an inertia valveto distinguish rider-induced forces from terrain-induced forces and isdescribed in U.S. Pat. No. 6,604,751 B2. According to U.S. Pat. No.6,604,751, the shock absorber of U.S. Pat. No. 6,604,751 is positionedbetween the swing arm and the main frame to provide resistance to thepivoting motion of the swing arm. The rear shock absorber includes aperipherally located fluid reservoir that is connected to the swing armat a distance away from the shock body, and is hydraulically connectedto the main shock body by a hydraulic hose. In one embodiment, thereservoir of U.S. Pat. No. 6,604,751 is connected to the swing armportion of the bicycle above the hub axis of the rear wheel.

The inertia valve assembly of U.S. Pat. No. 6,604,751 discloses aninertia valve attempting to overcome the effects of external forces andmanufacturing defects that inhibit the motion of the inertia valve withthe use of a labyrinth seal having a series of “Bernoulli Steps” on aninterior surface of the inertia mass. Also, the peripherally locatedreservoir of U.S. Pat. No. 6,604,751 discloses a blowoff valve thatallows for an increased flow rate after a minimum threshold pressure isexceeded inside the blowoff chamber. Typically, this will occur when thebicycle hits a severe bump. Further, the refill ports and the axialblowoff passages of the shock absorber of U.S. Pat. No. 6,604,751 arelocated on the top surface of the reservoir.

However, the need exists for an improved, lightweight rear inertia valveshock. The availability of lightweight, high performance inertia valveshocks are critical to competition cyclists, where a reduction of even afew ounces can greatly benefit the cyclist, and significantly impact thedesirability of the shock.

SUMMARY OF THE INVENTION

An aspect of one embodiment is a shock absorber for a bicycle comprisinga primary unit, a remote unit that is substantially entirely outside ofthe primary unit, and an inertial valve within the remote unit. Theprimary unit comprises a damper tube, a spring chamber, and a piston rodthat supports a main piston. The main piston is movable within thedamper chamber of the primary unit. The main piston and the damper tubeat least partially define a compression chamber. The remote unitcomprises a remote fluid chamber. The inertial valve is preferablyresponsive to terrain-induced forces and preferably not responsive torider-induced forces when the shock absorber is assembled to thebicycle. The shock absorber comprises a flow path separated from thepiston rod that connects the remote fluid chamber and the compressionchamber of the damper tube.

An aspect of one embodiment is a damper for a bicycle, comprising aprimary unit comprising a damper tube, a piston rod that supports a mainpiston, a reservoir tube that is outside of compression chamber of theprimary tube, and an inertia valve within the reservoir tube. The damperalso comprises a flow path connecting the reservoir fluid chamber andthe compression chamber of the primary tube. The main piston is movablewithin the damper chamber of the primary unit. The main piston and thedamper tube at least partially define a compression chamber and arebound chamber. The reservoir tube comprises a reservoir fluid chamber.At a piston speed of approximately 4 meters/second, at least 40% of thecompression damping in the reservoir tube occurs in a circuit which isnot closable by the inertia valve.

An aspect of one embodiment is a damper for a bicycle, comprising aprimary unit comprising a damper tube, a piston rod that supports a mainpiston, a reservoir tube that is outside of the compression chamber ofthe primary tube, and an inertial valve within the reservoir tube. Thedamper also comprises a flow path connecting the reservoir fluid chamberand the compression chamber of the primary tube. The damper alsocomprises a damping valve in the reservoir tube. When the inertia valveis open, the damping valve opens before flow through the inertia valveis maximized. The main piston and the damper tube at least partiallydefine a compression chamber and a rebound chamber. The main piston ismovable within the damper chamber of the primary unit. The reservoirtube comprises a reservoir fluid chamber. The inertial valve isresponsive to terrain-induced forces and not responsive to rider-inducedforces when the shock absorber is assembled to the bicycle.

An aspect of one embodiment is a damper for a bicycle, comprising aprimary unit comprising a damper tube, a piston rod that supports a mainpiston, a reservoir tube that is outside of compression chamber of theprimary tube, an inertial valve within the reservoir tube, a flowhousing within the reservoir tube, and a flow path connecting thereservoir fluid chamber and the compression chamber of the primary tube.The main piston is movable within the damper chamber of the primaryunit. The main piston and the damper tube at least partially define acompression chamber and a rebound chamber. The reservoir tube comprisesa reservoir fluid chamber. The flow housing defines a first end and asecond end, a first one way valve positioned at the first end, and asecond one way valve positioned at the second end. The inertia valve hasan open position and a closed position. The inertial valve permits aflow of the fluid from the compression chamber of the primary tube tothe reservoir fluid chamber of the reservoir tube when the inertialvalve is in the open position and the flow through the inertia valve isreduced when the inertia valve is in the closed position. In oneembodiment, the damping valve opens when there is 25 pounds of force onthe damping valve.

An aspect of one embodiment is a shock absorber for a bicycle comprisinga primary tube comprising a compression chamber and a spring chamber, apiston rod that supports a main piston, a remote tube that is separatefrom the primary tube, an inertial valve within the remote tube, a flowhousing, and a flow path connecting the remote fluid chamber and thecompression chamber of the primary tube. The main piston is movablewithin the compression chamber of the primary tube. The remote tubecomprises a remote fluid chamber. The flow housing defines a first endand a second end, a first one way valve positioned at the first end, anda second one way valve positioned at the second end. The inertial valveis responsive to terrain-induced forces and not responsive torider-induced forces when the shock absorber is assembled to thebicycle. The inertia valve has an open position and a closed positionand permits a flow of the fluid from the compression chamber of theprimary tube to the remote fluid chamber of the remote tube when theinertial valve is open and the flow through the inertia valve is reducedwhen the inertia valve is in the closed position.

An aspect of one embodiment is a shock absorber for a bicycle comprisinga primary tube comprising a compression chamber and a spring chamber, apiston rod that supports a main piston, a remote tube that is separatefrom the primary tube, an inertial valve within the remote tube, a shaftwithin the remote tube defining a plurality of flow ports and an outerannular groove connecting the plurality of flow ports, and a flow pathconnecting the remote fluid chamber and the compression chamber of theprimary tube. The main piston is movable within the compression chamberof the primary tube. The remote tube comprises a remote fluid chamber.The inertial valve is responsive to terrain-induced forces and notresponsive to rider-induced forces when the shock absorber is assembledto the bicycle. The inertia valve has an open position and a closedposition. The inertial valve permits a flow of the fluid from thecompression chamber of the primary tube to the remote fluid chamber ofthe remote tube when the inertial valve is open and the flow through theinertia valve is reduced when the inertia valve is in the closedposition.

An aspect of one embodiment is an inertia valve for a bicycle dampercomprising a reservoir shaft defining a first inside surface and anoutside surface, a groove formed in the outside surface of the reservoirshaft, a plurality of openings formed in the reservoir shaft between theinside surface and the outside surface, an inertia mass defining asecond inside surface that faces the outside surface of the reservoirshaft, and a spring. The inertia valve defines a closed position whereinthe second inside surface of the inertia mass substantially completelyprevents fluid from flowing through the plurality of openings. Theinertia mass also defines an open position wherein the fluid ispermitted to flow through any of the plurality of openings. The fluidflowing in an outward direction through any of the plurality of openingsflows into the groove. The inertia mass is biased toward the closedposition by the spring. The second inside surface of the inertia mass ispreferably spaced apart from the outside surface of the reservoir shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present bicycleshock absorber are described below with reference to drawings ofpreferred embodiments, which are intended to illustrate, but not tolimit, the present invention. The drawings contain sixteen (16) figures.Sixteen figures are described herein.

FIG. 1 is a perspective view of a bicycle including a preferred rearshock absorber;

FIG. 2 is a cross-section of the rear shock absorber of FIG. 1;

FIG. 3 is an exploded perspective view of the components of the rearshock absorber of FIG. 1;

FIG. 4 is an enlarged cross-section of a main portion of the shockabsorber of FIG. 2, showing the piston in an uncompressed position;

FIG. 5 is an enlarged cross-section of a main portion of the shockabsorber of FIG. 2, showing the piston in a partially compressedposition;

FIG. 6 is perspective view of the rebound side of a preferred pistoncomponent of the rear shock absorber of FIG. 1;

FIG. 7 is perspective view of the compression side of a preferred pistoncomponent of the rear shock absorber of FIG. 1;

FIG. 8 is an enlarged cross-section of a main portion of the shockabsorber of FIG. 1, showing the flow path of hydraulic fluid through thepiston during the compression motion of the rear shock;

FIG. 9 is an enlarged cross-section of a main portion of the shockabsorber of FIG. 1, showing the flow path of hydraulic fluid through thepiston during the rebound motion of the rear shock;

FIG. 10 is an enlarged cross-section of the reservoir of the shockabsorber of FIG. 1 showing an inertia valve in a closed position;

FIG. 11 is an exploded perspective view of the components of thereservoir of FIG. 1;

FIG. 12 is an enlarged cross-section of the reservoir of FIG. 1 showingthe inertia valve being in a closed position;

FIG. 13 is an enlarged cross-section of the reservoir of FIG. 1 showingthe flow path of hydraulic fluid through the primary valve during thecompression motion of the rear shock, the inertia valve being in aclosed position;

FIG. 14 is an enlarged cross-section of the reservoir of FIG. 1 showingthe flow path of hydraulic fluid through the primary valve during therebound motion of the rear shock, the inertia valve being in a closedposition;

FIG. 15 is an enlarged cross-section of the reservoir of FIG. 1 showingthe inertia valve being in an open position;

FIG. 16 is an enlarged cross-section of the reservoir of FIG. 1 showingthe flow path of hydraulic fluid through the inertia valve during thecompression motion of the rear shock, the inertia valve accordinglybeing in an open position;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a bicycle 20 (e.g., a mountain bike) having apreferred embodiment of a rear suspension assembly, or shock absorber,is illustrated. The bicycle 20 includes a frame 22, preferably comprisedof a generally triangular main frame portion 24 and an articulatingframe portion, or subframe 26, which is preferably pivotally connectedto the seat post tube 25 of the main frame portion 24. The bicycle 20also includes a front wheel 28 and rear wheel 30. The rear wheel 30 isconnected to the subframe portion 26. A seat 32, to provide support to arider in a sitting position, is connected to the seat post tube 25. Itis understood that in some embodiments, main frame portion 24 may not begenerally triangular or have a seat tube which extends uninterrupted tothe bottom bracket.

Positioned between the subframe 26 and the seat post tube 25 is apreferred embodiment of a rear shock 38. It is noted that, while theshock 38 disclosed herein is described in the context of its use as arear shock absorber for an off-road bicycle, the applicability of theinvention is not so limited. Aspects of the invention can be utilized inbicycle forks.

The rear shock 38 provides resistance to the pivoting motion of thesubframe 26, providing a suspension spring and damping to the motion ofthe subframe 26. Preferably, the spring is an air spring arrangement,but coil springs and other suitable arrangements may also be used. Thus,the bicycle 20 illustrated in FIG. 1 includes a rear shock 38 betweenthe rear wheel 30 and the frame 22. In this configuration, the rearshock 38 substantially reduces the magnitude of the impact forcesimparted on the rear wheel 30 by the terrain and felt by the operator ofthe bicycle. Referring to FIG. 2 the rear shock 38 desirably includes aprimary unit or main body portion 39 and a remote unit or secondary orreservoir body portion 44. Note that the reservoir body portion 44 maybe located adjacent to, or otherwise remote with respect to, the mainbody portion. However, in another embodiment, the reservoir body portionmay be located within the main body portion. In some embodiments, thefluid reservoir body portion 44 is directly connected to the main bodyportion 39 external to the main body portion 39.

As is discussed in detail below, the inertia valve described herein mayadvantageously be configured to be highly responsive to changes in theacceleration of the rear shock 38. Further, in some embodiments, theinertia valve components described herein are relatively easy and costeffective to produce, resulting in low manufacturing costs and fewproduction errors. As discussed, the rear shock 38 preferably includesan inertia valve 138 that varies the damping rate of the rear shock 38depending upon the direction of an acceleration of the inertia valve138. In this configuration, the inertia valve 138 can distinguishbetween forces imparted on the rear wheel 30 originating from the riderof bicycle from forces imparted on the rear wheel 30 by bumps in thepath of travel. Performance of the bicycle is improved when forcesgenerated by the rider are more firmly damped and forces imparted on therear wheel 30 by bumps in the road are damped more softly. This reducesor prevents shock absorber movement resulting from rider-induced forces,such as by pedaling, while allowing the shock absorber to compensate forforces imparted on the rear wheel 30 by uneven terrain. It is understoodthat in some embodiments, the shock absorber will move very little inresponse to rider induced pedal forces.

A preferred embodiment of the rear shock 38 is illustrated in FIGS.2-16. Generally, the rear shock 38 comprises a spring, a main pistonassembly, and a reservoir. In one embodiment, the spring comprises anair spring formed by an air tube 40 and a spring piston comprising aseal formed on the exterior of a hydraulic fluid body portion 42. In theillustrated embodiment, reservoir body portion 44 is external to themain body portion 39 but is directly connected to the hydraulic fluidbody portion 42 without long external passages, hydraulic hoses, or thelike. The connection between the reservoir body portion 44 and the mainbody of the shock 38 can be achieved by any suitable means, such as by,but not limited to, threading or press-fitting the reservoir bodyportion 44 into the hydraulic fluid body portion 42. Alternatively, thereservoir body portion 44 can be monolithically formed with thehydraulic fluid body portion 42.

FIG. 3 is an exploded perspective view of the components that comprisethe main body portion 39 of the rear shock 38. Preferably, the main bodyportion 39 is generally comprised of a main piston or hydraulic fluidbody portion 42, a spring or air tube 40 closed by an upper cap 50, apiston 68, and a hydraulic fluid body portion cap 72. The hydraulicfluid body portion 42 may be cylindrical in shape and includes an openend portion 54 and a lower closed end portion 56. The lower closed endportion 56 has a lower eyelet 58 that is used for connecting the shock38 to the subframe portion 26 of the bicycle 20 of FIG. 1.

FIG. 1 illustrates an embodiment of the rear shock 38 mounted in itspreferred configuration to the main frame portion 24 (using upper eyelet52) and the subframe portion 26 (using lower eyelet 58) of the bicycle20. With reference to FIGS. 1 and 3, it can be seen that the mountingplanes of the upper eyelet 52 and the lower eyelet 58, respectively, arenot coplanar. The mounting plane of the lower eyelet 58 is clocked at adifferent orientation with respect to the mounting plane of the uppereyelet 52 because, as illustrated in FIG. 1, the subframe mounting tab26 a is positioned at a different orientation as compared to themounting plane on the main frame portion 24. However, while theorientation of the mounting plane of the lower eyelet 58 is not coplanarwith the orientation of the mounting plane of the upper eyelet 52 in theembodiment illustrated in FIGS. 1-3, the respective orientations of theeyelets 52, 58 is not so limited. The mounting planes of the eyelet 52,58 can be clocked at any orientation suitable for the frame to which therear shock 38 is mounted.

The air tube 40 may also be cylindrical in shape. The air tube 40includes an open end 48. The opposite end is closed by an upper cap 50.The upper cap 50 of the air tube 40 has an elongated portion 51 and anupper eyelet 52. The upper eyelet 52 is used to connect the rear shock38 to the seat post tube 25 of the bicycle 20. The open end 48 of theair tube 40 slidingly receives the hydraulic fluid body portion 42. Inthis configuration, the air tube 40 and the hydraulic fluid body portion42 are configured for telescopic movement between the main frame portion24 and the subframe portion 26 of the bicycle 20.

In another embodiment, the orientation of the rear shock 38 may bechanged such that the hydraulic fluid body portion 42 is attached to theseat post tube 25 (at the lower eyelet 58) while the air tube 40 isattached to the subframe 26 (at the upper eyelet 52). However, this isnot preferred.

The air tube 40 has a seal assembly 60 positioned at the open end 48thereof, forming a substantially airtight seal between the hydraulicfluid body portion 42 and the air tube 40. In the illustratedembodiment, the seal assembly 60 is comprised of an annular seal bodyseal 62 having a substantially square cross-section that is locatedbetween a pair of bearings 64. A wiper 66 is located adjacent the openend 48 of the air tube 40 to prevent dust, dirt, rocks, and otherpotentially damaging debris from entering into the air tube 40 as thehydraulic fluid body portion 42 moves into the air tube 40. A pistonmember 68 is positioned within and slides relative to the inner surfaceof the hydraulic fluid body portion 42. The piston member 68 isconnected to the upper cap 50 by a shock shaft 70, fixing the pistonmember 68 for motion within the air tube 40.

As most clearly illustrated in FIG. 4, a hydraulic fluid body portioncap 72 is fixed to the open end portion 54 of the hydraulic fluid bodyportion 42 and is configured to allow the shock shaft 70 to slide withina central opening in the hydraulic fluid body portion cap 72. Thehydraulic fluid body portion cap 72 accordingly slides within the innersurface of the air tube 40. Because the hydraulic fluid body portion cap72 is easier to manufacture in two portions, the hydraulic fluid bodyportion cap 72 is preferably comprised of an upper cap portion 72 a anda lower cap portion 72 b. After the lower cap portion 72 b is insertedover the end of the hydraulic fluid body portion 42, the upper capportion 72 a is preferably fixed to the hydraulic fluid body portion 42by threading the upper cap portion 72 a into threads formed on theinside surface of the hydraulic fluid body portion 42. The upper capportion 72 a and lower cap portion 72 b are configured such that, whenthe upper cap portion 72 a is attached to the hydraulic fluid bodyportion 42 as described above, the lower cap portion 72 b will also befirmly attached to the hydraulic fluid body portion 42. Annular seals82, 83 are preferably used to prevent hydraulic oil from leaking intothe primary air chamber 86 and, similarly, to prevent the gas located inthe primary air chamber 86 from leaking into the compression chamber 96.

A seal assembly 74 is preferably positioned on the hydraulic fluid bodyportion cap 72. The seal assembly 74 is preferably comprised of a sealmember 76, which is preferably an annular seal having a substantiallyround cross-section and is positioned between a pair of bearings 78, anda bushing 84. Together, the seal member 76 and the bushing 84 create aseal between the hydraulic fluid body portion cap 72 and the shock shaft70, while allowing the shock shaft 70 to translate within the hydraulicfluid body portion cap 72. Note that the cross-section of the sealmember 76 may be any suitable shape, such as square or rectangular.

A bottom out bumper 92 is desirably positioned near the closed endportion 50 of the air tube 40 to prevent direct metal to metal contactbetween the closed end portion 50 and the hydraulic fluid body portioncap 72 of the hydraulic fluid body portion 42 upon full compression ofthe rear shock 38. The bottom out bumper 92 is preferably formed from asoft, pliable, and resilient material, such as rubber. The bottom outbumper 92 is positioned between two washers 94 a, 94 b, which hold thebottom out bumper 92 in position next to the closed end portion 50.Washers 94 a, 94 b can also be formed from a soft, pliable, andresilient material, such as rubber. Similarly, an annular rebound bumper89 is preferably positioned around the outside of the hydraulic fluidbody portion 42 below the hydraulic fluid body portion cap 72, but abovethe bearings 64. The rebound bumper 89 prevents metal to metal contactbetween the bottom portion of the hydraulic fluid body portion cap 72and the constricted portion of the air tube 40, and buffers themagnitude of the impact between the two components, at the end of therebound motion of the rear shock 38.

The space between the hydraulic fluid body portion cap 72 and the sealassembly 60 defines a second air chamber 88. Air chamber 88 is mostclearly illustrated in FIG. 5, which illustrates the main body of therear shock 38 in a partially compressed state. Air that fills the secondair chamber 88 exerts a pressure that resists the rebound motion of therear shock 38. Rebound motion is defined as the motion of the rear shock38 that occurs when the shock 38 extends axially such that the closedends 56 and 50 of the hydraulic fluid body portion 42 move away fromeach other. In conjunction, the primary air chamber 86 and the secondair chamber 88 form the suspension spring portion of the rear shock 38.An air valve 90 (see FIGS. 2-3) communicates with the primary airchamber 86 to allow the air pressure therein to be adjusted. In thismanner, the spring rate of the rear shock 38 may be easily adjusted.

The primary air chamber 86 is defined as the space between the closedend portion 50 of the air tube 40 and the hydraulic fluid body portioncap 72. Air held within the primary air chamber 86 exerts a biasingforce to resist compression motion of the rear shock 38. Compressionmotion is defined as the motion of the rear shock 38 that occurs whenthe closed ends 56 and 50 of the hydraulic fluid body portion 42 and airtube 40 (and thus the eyelets 52, 58) move closer to one another.

The hydraulic fluid body portion 42 of the rear shock 38 will now bedescribed in detail. The interior chamber of the hydraulic fluid bodyportion 42 is divided by the piston member 68 into two portions. Thefirst portion is the compression chamber 96. The second portion is therebound chamber 98. The rebound chamber 98 is defined to be the spacebetween the piston member 68 and the hydraulic fluid body portion cap72. The rebound chamber 98 increases in volume during the compressionmotion of the rear shock 38, and decreases in volume during the reboundmotion of the rear shock 38. The compression chamber 96 is defined asthe space between the piston member 68 and the closed end portion 56 ofthe hydraulic fluid body portion 42. The compression chamber 96decreases in volume during compression motion of the rear shock 38, anddecreases in volume during the rebound motion of the rear shock 38. Asis stated above, FIG. 4 illustrates an embodiment of the rear shock 38wherein the piston 68 is in an uncompressed state. FIGS. 5, 8, and 9illustrate an embodiment of the rear shock 38 wherein the piston 68 isin a partially compressed state.

As most clearly seen in FIG. 4, a hollow threaded fastener 100 fixes thepiston member 68 to the shock shaft 70. A seal 102, of an annular typehaving a rectangular cross-section, is attached to the piston member 68and seals the piston 68 with the inner surface of the hydraulic fluidbody portion 42.

In the illustrated embodiment, the piston member 68 preferably includesa plurality of compression flow passages 104, each compression flowpassage 104 preferably having an elongated shape. The plurality ofcompression flow passages 104 are most clearly seen in FIGS. 6 and 7. Invarious embodiments, the compression flow passages 104 may cumulativelyperforate and, hence, allow the passage of hydraulic fluid through 10%to 60%, 15% to 40%, or 20% to 35% of included cross-sectional area ofthe piston 68. As used herein, “included cross-sectional area” means thecross-sectional within the periphery of the piston member 68 in a planeperpendicular to the axis. In the case of the piston member 68, the axisis aligned with the shock shaft 68). The compression flow passages 104may cumulatively perforate and allow the passage of hydraulic fluidthrough at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% and60% of the included cross-sectional area.

The compression flow passages 104 are covered on the rebound chamber 98side of the piston member 68 by a shim stack 106. The shim stack 106 canbe made up of one or more flexible, preferably annular, shims. The shimstack 106 preferably operates as a one-way check valve—deflecting toallow a flow path of minimal restriction through the compression flowpassages 104 during compression motion of the rear shock 38, whilepreventing flow through the compression flow passages 104 during therebound motion of the rear shock 38. In the illustrate configuration,the shim stack 106 is preferably made up of multiple shims having arange of thicknesses, stiffnesses, and diameters that are preferablyeasily deflected to allow hydraulic fluid to flow with minimalrestriction through compression flow passages 104 during compressionmotion of the rear shock 38. The substantially unrestricted flow path ofhydraulic fluid (represented by arrows) through the compression flowpassages 104 and the deflection of the shim stack 106 during thecompression motion of the rear shock 38 are illustrated in FIG. 8. FIG.8 also illustrates the flow of hydraulic fluid out of the secondarypassage 113 into the rebound chamber 98. For this flow path, thehydraulic fluid flows from the compression chamber 96 through the hollowpin 100 and the central passage 112 before flowing out of the secondarypassage 113 and into the rebound chamber 98.

As most clearly seen in FIGS. 6 and 7, the piston member 68 shown in theillustrated embodiment also comprises a plurality of rebound flowpassages 108, preferably three, through the piston member 68. Therebound flow passages 108 preferably have axial through holes 108 a andplanar channels 108 b. The planar channels 108 b are formed on therebound side of the piston member 68 and permit fluid to bypass thecompression shim stack 106 during the rebound motion of the rear shock38. As such, the hydraulic oil flows through both the planar channels108 b and the axial through holes 108 a during the rebound motion of therear shock 38. A notable advantage of this configuration is that thesize of the compression flow passages 104 can be increased to permit avery high flow rate of hydraulic fluid through the piston 68 during thecompression motion without otherwise limiting the size of the, and,hence, the amount of fluid that can flow through the, rebound flowpassages 108 that may otherwise be required if the planar channels 108 bwere not present. This also permits the piston member 68 to be formedfrom a single piece of material, instead of a multi-piece or cup design.

In certain embodiments, the rebound flow passages 108 may cumulativelyperforate and, hence, allow the passage of hydraulic fluid through 2% to25%, 5% to 15% to 5% to 10% of the included cross-sectional area. Therebound flow passages 108 may cumulatively perforate and, hence, allowthe passage of hydraulic fluid through no more than 2%, 5%, 10% or 15%of the included cross-sectional area.

A rebound shim stack 110, which can be made up of one or more flexibleshims, is preferably positioned on the compression side of the pistonmember 68 adjacent to the planar channels 108 b. The rebound shim stack110 deflects to allow, but to control the amount of, flow through therebound flow passages 108 during the rebound motion of the rear shock38. The rebound shim stack 110 prevents flow through the rebound flowpassages 108 during the compression motion of the rear shock 38, but ispreferably configured to not obstruct the flow of hydraulic oil throughthe more outwardly located compression flow passages 104 duringcompression motion. As such, the rebound shim stack 110 provides dampingto the flow of hydraulic fluid through the piston 68 during the reboundmotion of the rear shock 38.

FIG. 9 illustrates the damped flow path of hydraulic fluid (representedby arrows) from the rebound chamber 98 through the rebound flow passages108, as well as the deflection of the shim stack 110, during the reboundmotion of the rear shock 38. FIG. 9 also illustrates the flow ofhydraulic fluid from the rebound chamber 98, through the secondarypassage 113, the central passage 112, and the hollow pin 100 into thecompression chamber 96.

The shock shaft 70 defines a central passage 112 therethrough. Thecentral passage 112 is in communication with the compression chamber 96through the hollow pin 100. The interior chamber of the reservoir bodyportion 44 also communicates with the compression chamber 96 through apassage 114 that goes through the closed end portion 56 of the hydraulicfluid body portion 42 of the main body portion 39. This permitshydraulic fluid to flow between the reservoir body portion 44 and thecompression chamber 96.

As seen most clearly in FIGS. 8 and 9, a secondary passage 113 throughthe shock shaft 70 provides a port through which hydraulic fluid mayflow between the central passage 112 and the compression chamber 96 whenthe shock is partially to fully compressed. When the rear shock 38 is inits substantially uncompressed state, as illustrated in FIG. 4, thebushing 84 and plate 115 substantially prevent the hydraulic fluid fromflowing through the secondary passage 113 into the rebound chamber 98.

An adjustment rod 116 is positioned concentrically within the centralpassage 112 of the shock shaft 70, extending from the closed end portion50 of the air tube 40. The adjustment rod 116 is preferably configuredto alter the damping force in the rear shock 38 by altering the amountof fluid that can flow through the secondary passage 113 uponcompression motion and rebound motion. This is achieved by adjusting theadjustment rod 116 such that the annular ring 116 a partially or fullyblocks the secondary passage 113, thus partially or fully preventingfluid from flowing through the secondary passage 113. However, becausein the configuration of the main body portion 39 illustrated in FIGS.2-9, the compression flow passages 104 allow significantly more flowvolume therethrough as compared to the rebound flow passages 108, theadditional volume of fluid that is permitted to flow through secondarypassage 113 more significantly affects the rebound motion than thecompression motion of the rear shock 38.

Thus, while adjustment of the adjustment rod 116 alters fluid flow fromthe compression chamber 96 to the rebound chamber 98 during bothcompression motion and rebound motion, the adjustment rod 116 moresignificantly adjusts the fluid flow from the compression chamber 96 tothe rebound chamber 98 during the rebound motion of the rear shock 38.The rebound damping, as compared to the compression damping, is moregreatly affected by the adjustment of the adjustment rod 116 for thefollowing reason. Barring from consideration the flow restrictionprovided by the various shim stacks, as discussed above, the compressionflow passages 104 are desirably configured to allow a greater flow ratetherethrough as compared to the rebound flow passages 108. This isbecause, as discussed above, the cumulative size of the openingscomprising the compression flow passages 104 is desirably significantlygreater than the cumulative size of the openings comprising the reboundflow passages 108.

Further, the size of the opening comprising the secondary passage 113 ispreferably much less than the cumulative size of the openings comprisingthe compression flow passages 104. In certain embodiments, the size ofthe opening comprising the secondary passage 113 can be 2% to 30%, 5% to25%, 10% to 20% of the cumulative cross-sectional area of the openingscomprising the compression flow passages 104. In certain embodiments,the size of the opening comprising the secondary passage 113 no morethan 30%, 25%, 15%, 10%, 5% of the cumulative cross-sectional area ofthe openings comprising the compression flow passages 104. Thus, theadditional flow through the secondary passage 113 does not significantlyincrease the flow from the compression chamber 96 to the rebound chamber98 during the compression motion of the rear shock 38.

Similarly, the size of the opening comprising the secondary passage 113is preferably less than the cumulative cross-sectional area of theopenings comprising the rebound flow passages 108. In certainembodiments, the cross-sectional area of the opening comprising thesecondary passage 113 can be approximately 15% to approximately 35% ofthe cumulative cross-sectional area of the openings comprising therebound flow passages 108. In certain embodiments, the cross-sectionalarea of the opening comprising the secondary passage 113 is no more than25% of the cumulative cross-sectional area of the openings comprisingthe rebound flow passages 108. In sum, because the ratio of the size ofthe secondary passage 113 to the size of the openings comprising therebound flow passages 108 is greater than the ratio of the size of thesecondary passage 113 to the size of the openings comprising thecompression flow passages 104, allowing flow through the secondarypassage 113 will more significantly affect the net overall flow duringthe rebound motion of the rear shock 38 as compared to the compressionmotion of the rear shock 38. Therefore, adjustments to the adjustmentrod 116 will preferably have a greater effect on rebound damping ascompared to compression damping of the rear shock 38.

As such, the adjustment rod 116 provides the user of the rear shock 38with the ability to adjust the rebound damping of the rear shock 38. Anadjustment dial 118, which is attached to the end of the reboundadjustment rod 116, allows a user to adjust the adjustment rod 116 and,hence, the rebound damping rate of the rear shock 38. The adjustmentdial 118 is located on the outside of the rear shock 38. Thus, it iseasily accessible by the user. A ball detent mechanism 120 providesdistinct adjustment positions of the adjustment dial 118.

It is noted that, while the central passage 112 may be described ashaving a secondary passage 113, the annular ring 116 a of the adjustmentrod 116 desirably does not completely prevent flow through the secondarypassage 113 even in the fully blocked or closed position. That is, afluid-tight seal is not typically created between the annular ring 116 aof the adjustment rod 116 and the secondary passage 113 even in thefully blocked or closed position. Thus, some fluid may flow through thesecondary passage 113 in its closed position. Such fluid flow is oftenreferred to as “bleed flow” and, preferably, is limited to a relativelysmall flow rate. To create a fluid-tight seal between theabove-referenced components would require precise dimensionaltolerances, which would be expensive to manufacture, and may alsoinhibit movement of the adjustment rod 116 in the central passage 112.

With reference to FIGS. 10 through 16, the components of the reservoirbody portion 44 will now be described. FIG. 11 is an explodedperspective view of the components that comprise the reservoir bodyportion 44 of the rear shock 38. As most clearly shown in FIG. 10, thereservoir body portion 44 includes a reservoir tube 122. The reservoirtube 122 is closed on both ends thereof. A floating reservoir piston 124is positioned inside of the reservoir tube 122 and is in slidingcommunication with an inside surface of the reservoir tube 122. Asubstantially fluid-tight seal between the interior surface of thereservoir tube 122 and the reservoir piston 124 is provided by the sealmember 126. Although other suitable seals may also be used, the sealmember 126 is preferably a substantially round cross-section, annularseal. A low friction bushing 123 helps align the reservoir piston 124 ona reservoir adjustment rod 184.

The interior space of the reservoir tube 122 is divided into a reservoirchamber 128 and a gas chamber 130 by the floating reservoir piston 124.An end cap 132 closes the reservoir chamber 128 portion of the reservoirtube. A connector 133 attached to the end cap 132 allows the reservoirbody portion 44 to interface with the closed end portion 56 of thehydraulic fluid body portion 42 so that hydraulic fluid can flow fromthe passage 114 in the closed end portion 56 of the hydraulic fluid bodyportion 42 to the reservoir chamber 128 of the reservoir body portion44. In this configuration, the passages 112 and 114 are in fluidcommunication with the central passage 136 of the reservoir shaft 134,as well as with the compression chamber 96.

An inertia valve assembly 138 is also supported by the reservoir shaft134. When in the open configuration, as illustrated in FIGS. 15 and 16,the inertia valve assembly 138 permits communication between thereservoir chamber 128 and the compression chamber 96 via the passages114 and 136. Stated another way, when the inertia valve assembly 138 isin the open configuration, hydraulic fluid is permitted to flow from thecompression chamber 96 through the passage 114 and passage 136, and outthrough reservoir shaft fluid ports 148 into the reservoir chamber 128.

Cap 142 closes the gas chamber 130 end of the reservoir tube 122. Thecap 142 includes a valve assembly 144 to add or remove gas, such asnitrogen, for example, to or from the gas chamber 130. The positivepressure exerted on the floating reservoir piston 124 by the pressurizedgas within the gas chamber 130 causes the floating reservoir piston 124to exert a pressure on the hydraulic fluid in the reservoir chamber 128.In this configuration, the positive pressure causes the gas chamber 130to expand to include any space made available when hydraulic fluid flowsfrom the reservoir chamber into the compression chamber. It alsoimproves the flow of fluid from the reservoir body portion 44 into theinto the compression chamber 96 during the rebound motion of the rearshock 38.

Referring to FIGS. 10 and 11, a primary valve assembly 140 is positionedabove the inertia valve assembly 138 and is carried by the reservoirshaft 134. A shoulder portion 154 is defined where the reservoir shaft134 reduces in diameter. The shoulder 154 supports an annular washer156. The annular washer 156 supports the primary valve assembly 140. Thewasher 156 also provides a buffer between the inertia mass 150 and theprimary valve assembly 140.

As is clearly illustrated in FIG. 12, the primary valve assembly 140 isgenerally comprised of a cylindrical base 158 and a cap 160. The cap 160is preferably threadably engaged with the base 158 and supported by anupper surface 164 of the base 158. A cap seal 166 seals the cap 160 tothe inner surface of the base 158. The cap seal 166 is preferably anannular ring with a round cross-section, but the cap seal 166 can haveany suitable configuration. The cap 160 is preferably threadablyfastened to the base 158. The base 158 is attached to the reservoirshaft 134 by a threaded fastener 168. A primary valve chamber 170 isdefined as the space between the cap 160 and the base 158. The reservoirshaft 134 partially extends into the primary valve chamber 170 and hasan open end such that the passage 136 is in communication with theprimary valve chamber 170.

The cap 160 has one or more axial compression flow passages 174. Thebase 158 has one or more axial refill ports 176. Because the axialrefill passages are located in the base 158 and not in the cap 160(where the compression flow passages 174 are located), the geometricconfiguration of the cap 160 is advantageously simplified. A furtheradvantage of having the refill ports 176 in the base 158 as opposed tohaving them in the cap 160 along with the compression flow passages 174is that the size of either the refill ports 176 or the compression flowpassages 174 will not be constrained by the size limitations of the cap160. A compression flow shim stack 178, which covers the compressionflow passages 174, is located above the cap 160. A threaded fastener 169secures the compression flow shim stack 178 in place. Once the threadedfastener 169 is threaded into the cap 160, it can be held in place withan adhesive or other suitable material to prevent it from loosening. Aswill be discussed below, the threaded fastener 169 also comprises ableed valve port 171 which adjustably provides another flow path forhydraulic fluid to flow from the primary valve chamber 170 to thereservoir chamber 128. As discussed below, adjustment of the bleed valveport 171 adjusts the stiffness of the rear shock 38.

As stated above, the illustrated embodiment preferably comprises acompression flow shim stack 178 to regulate the flow rate of hydraulicfluid through the compression flow passages 174. In one embodiment,between 50 lbs and 75 lbs of force is required to be exerted on thecompression flow shim stack 178 in order to deflect the compression flowshim stack 178 enough to allow the hydraulic fluid to flow through thecompression flow passages 174 at a rate that allows the piston 68 tomove within the hydraulic fluid body portion 42 at a rate ofapproximately 0.05 m/s. In another embodiment, between 25 lbs and 50 lbsof force is required to be exerted on the compression flow shim stack178 in order to allow the piston 68 to move within the hydraulic fluidbody portion 42 at a rate of approximately 0.05 m/s.

In certain embodiments, when there is 25 lbs, 35 lbs, 45 lbs, 55 lbs, 65lbs or 75 lbs of force exerted on the compression flow shim stack 178,the shim stack 178 deflects thereby opening the damping valve.Specifically, the compression flow shim stack 178 deflects enough toallow the piston 68 to move within the hydraulic fluid body portion 42at a rate of approximately 0.05 meters/sec.

However, to regulate the flow rate of hydraulic fluid through thecompression flow passages 174, a flow element having a series of portsmay be substituted for the shim stack 178. In general, any of the shimstacks described herein may be replaced or augmented with a flow elementhaving a series of ports for the purpose of regulating the flow rate ofhydraulic fluid through the various components comprising the rear shock38.

The axial compression flow passages 174 may cumulatively perforate and,hence, allow the passage of hydraulic fluid through, 10% to 50%, or 25%to 35%, of the included surface area of the cap 160. The axial refillports 176 may cumulatively perforate and, hence, allow the passage ofhydraulic fluid through, 10% to 50% or more of the included surface areaof the base 158. The axial refill ports 176 may cumulatively perforateand allow the passage of hydraulic fluid through 2% to 25% of theincluded surface area of the base 158. The axial refill ports 176 maycumulatively perforate and allow the passage of hydraulic fluid throughthe base 158 at a flow rate approximately equal to the amount of flow ofhydraulic fluid that is flowing through passage 114, i.e., approximatelyequal to the amount of flow of hydraulic fluid that is flowing from thereservoir body portion 44 to the main body portion 39.

In one embodiment, the compression flow shim stack 178 is configured todeflect to allow, but damp the flow rate of, hydraulic fluid through thecompression flow passages 174 at normal operating pressures of the rearshock 38. In certain embodiments, each of the shims comprising thecompression flow shim stack 178 is preferably a bendable disc made froma metallic alloy. In one embodiment, five shims that are approximately16 mm in diameter and 0.15 mm thick, stacked together, would produce acompression damping force of approximately 75-80 lbs at a rate of fluidflow that allows the piston 68 to move within the hydraulic fluid bodyportion 42 at a rate of approximately 0.05 m/s. In another embodiment,four shims that are approximately 16 mm in diameter and 0.15 mm thick,stacked together, would produce a compression damping force ofapproximately 65-70 lbs at a rate of fluid flow that allows the piston68 to move within the hydraulic fluid body portion 42 at a rate ofapproximately 0.05 m/s. In another embodiment, three shims that areapproximately 16 mm in diameter and 0.15 mm thick, stacked together,would produce a compression damping force of approximately 55-60 lbs ata rate of fluid flow that allows the piston 68 to move within thehydraulic fluid body portion 42 at a rate of approximately 0.05 m/s. Inanother embodiment, two shims that are approximately 16 mm in diameterand 0.15 mm thick, stacked together, would produce a compression dampingforce of approximately 45-50 lbs at a rate of fluid flow that allows thepiston 68 to move within the hydraulic fluid body portion 42 at a rateof approximately 0.05 m/s, and so on.

The compression flow shim stack 178 of the present invention operates todamp the compression motion of the rear shock 38 and, accordingly, canbe configured to deflect to allow hydraulic fluid to flow through thecompression flow passages 174 at low or regular operating pressureswithin the primary valve chamber 170. In one embodiment, approximately90% or more of the compression motion damping of the rear shock isaccomplished by the compression flow shim stack 178 located in thereservoir body portion 44, whereas the remainder of the compressionmotion damping of the rear shock is accomplished by other components ofthe rear shock (e.g., the compression shim stack 106 located in the mainbody portion 39). In another embodiment, approximately 80% or more ofthe compression motion damping of the rear shock is accomplished by thecompression flow shim stack 178 located in the reservoir body portion44. In yet another embodiment, approximately 70% or more of thecompression motion damping of the rear shock is accomplished by thecompression flow shim stack 178 located in the reservoir body portion44. In yet another embodiment, approximately 50% or more of thecompression motion damping of the rear shock is accomplished by thecompression flow shim stack 178 located in the reservoir body portion44.

As illustrated in FIGS. 10 and 12, a bleed valve plug 182 extendsdownwardly from below the reservoir piston 124, and threads into acylindrical interior threaded surface of the threaded fastener 169. Thereservoir adjustment rod 184 preferably inserts into the bleed valveplug 182 such that the bleed valve plug 182 is in rotationalcommunication with the reservoir adjustment rod 184. On its other end,the reservoir adjustment rod 184 is preferably attached to a reservoiradjustment dial 185. The reservoir adjustment dial 185 is incommunication with, but is free to rotate relative to, the cap 142. Inparticular, a clip 189 inserted into a circumferential groove in thevalve post 191 holds the reservoir adjustment dial 185 in communicationwith the cap 142. A ball detent mechanism 187 provides distinctadjustment positions of the reservoir adjustment dial 185.

Further, the bleed valve plug 182 defines a tip 182 a that preferablyadjustably regulates the flow of hydraulic fluid through a metering rodflow port 186 located in the end of the threaded fastener 169. The tip182 a preferably defines a conically shaped surface that tapers to asmaller cross-sectional diameter toward the bottom end of the tip 182 a.The largest diameter of the conical portion is greater than the diameterof the cylindrical metering rod flow port 186, and the smallest diameterof the conical portion is smaller than the diameter of the cylindricalmetering rod flow port 186. In this configuration, the flow of hydraulicoil through the metering rod flow port 186 can be reduced by engagingthe tip 182 a of the bleed valve plug 182 into the metering rod flowport 186. Accordingly, the flow of hydraulic oil through the meteringrod flow port 186 can be substantially prevented by fully engaging thetip 182 a of the bleed valve plug 182 into the metering rod flow port186. However, some amount of flow may occur through a clearance spacebetween the tip 182 a and the metering rod flow port 186, which mayoccur due to normal manufacturing variations.

As most clearly illustrated in FIG. 12, in this configuration, as thereservoir adjustment dial 185 is turned either clockwise orcounter-clockwise, the axial position of the bleed valve plug 182 ispreferably moved either up or down relative to the threaded fastener169, respectively, within the interior threaded surface of the threadedfastener 169. As the bleed valve plug 182 is moved down relative to thethreaded fastener 169, the bleed valve plug 182 progressively blocks thebleed valve port 171 and metering rod flow port 186, though notnecessarily simultaneously. Thus, as the bleed valve plug 182 is rotatedfurther into the threaded fastener 169, the flow of hydraulic fluidthrough the bleed valve port 171 is substantially cut off. Because thebleed valve port 171 provides another, albeit more constricted, flowpath for hydraulic fluid to flow from the primary valve chamber 170 intothe reservoir chamber 128, cutting off the flow of hydraulic fluidthrough the bleed valve port 171 effectively makes the rear shock 38stiffer during the compression motion of the rear shock 38.

In the illustrated embodiment, a single shim comprising the rebound flowshim stack 180 is preferably located between an annular ring 179 and thebase 158. However, the rebound flow shim stack 180 is not so limited.The rebound flow shim stack 180 can be comprised of multiple shims,similar to the compression flow shim stack 178 described above, and thereservoir body portion 44 may or may not have the annular ring 179. Therebound flow shim stack 180 covers the refill ports 176. The reboundflow shim stack 180 substantially prevents fluid from flowing from theprimary valve chamber 170 to the reservoir chamber 128 through refillports 176, while not significantly affecting the rate of fluid flow fromthe reservoir chamber 128 into the primary valve chamber 170. I.e., therebound flow shim stack 180 prevents hydraulic fluid flow through refillports 176 during the compression motion of the rear shock 38, but doesnot substantially affect the flow rate of hydraulic fluid through therefill ports 176 during the rebound motion of the rear shock 38.

In the illustrated embodiment, the damping control of the rebound motionof the rear shock 38 is advantageously located in the main shock body ofthe rear shock 38, as opposed to being located in the reservoir bodyportion 44 as in other, conventional designs. Because the flowrestriction, or damping, is located in the main shock body of the rearshock 38, the flow of hydraulic fluid into the compression chamber 96 isnot disturbed by cavitation or other flow disrupting effects that oftenresult when the hydraulic fluid is sucked or pulled through the flowrestriction devices or shim stacks that are located in the reservoirs ofother, conventional designs. In the illustrated embodiment, during therebound motion of the rear shock, a compressive force pushes thehydraulic fluid located in the rebound chamber 98 through the reboundflow passages 108, thus avoiding cavitation and other flow efficiencyeffects that may otherwise result.

In certain embodiments, at least 90%, at least 80%, at least 70%, atleast 60% or at least 50% of the rebound motion damping of the rearshock 38 is accomplished in the main body portion 39, whereas theremainder of the rebound damping of the rear shock is accomplished byother components of the rear shock (preferably in the reservoir bodyportion 44). In one embodiment, this rebound damping in the main bodyportion 39 can be substantially accomplished by the rebound shim stack110 located in the main body portion 39.

FIG. 14 illustrates the flow of hydraulic fluid from the reservoirchamber 128, around the cap 160 and the base 158 and through the reboundflow passages 176 and into the passage 136, as well as the correspondingpreferred deflection of the rebound flow shim stack 180, when theinertia valve 138 is in the closed position.

As most clearly illustrated in FIG. 16, a plurality of radiallyextending reservoir shaft fluid ports 148, each having a generallycylindrical geometry, extend through the reservoir shaft 134. Thereservoir shaft fluid ports 148 connect the passage 136 to the reservoirchamber 128. As mentioned above, the inertia valve assembly 138 alsoincludes an inertia mass 150 that is disposed in an upward position by aspring 152, as is shown in FIGS. 10 and 12-14.

The diameter of each reservoir shaft fluid port 148 may be between 0.5mm and 5.0 mm. As illustrated, the reservoir shaft 134 preferably has atotal of four equally spaced reservoir shaft fluid ports 148, each witha diameter equal to approximately 1.0 mm. In another embodiment, thediameter of each reservoir shaft fluid port 148 is approximately 1.5 mmor more. In another embodiment, the diameter of each reservoir shaftfluid port 148 is approximately 2.0 mm or more. In another embodiment,the diameter of each reservoir shaft fluid port 148 is approximately 3.0mm or more. In yet another embodiment, the diameter of each reservoirshaft fluid port 148 is approximately 4.0 mm or more. In anotherembodiment, the diameter of each reservoir shaft fluid port 148 isapproximately 5.0 mm or more. In another embodiment, the reservoir shaft134 may have six or more reservoir shaft fluid ports 148, regardless ofthe diameter of the reservoir shaft fluid ports 148. In certainembodiments, the total cross-sectional area of the reservoir shaft fluidports 148 is 2 square millimeters to 100 square millimeters, 2 squaremillimeters to 80 square millimeters, 2 square millimeters to 60 squaremillimeters, 2 square millimeters to 40 square millimeters, 2 squaremillimeters to 20 square millimeters, 2 square millimeters to 10 squaremillimeters, or 2 square millimeters to 5 square millimeters. In certainembodiments, the total cross-sectional area of the reservoir shaft fluidports 148 is no more than 12 square millimeters, no more than 10 squaremillimeters, no more than 8 square millimeters, no more than 6 squaremillimeters, or no more than 5 square millimeters.

Furthermore, in one embodiment, when the rear shock 38 encounters a bumpthat causes the piston 68 to move within the hydraulic fluid bodyportion 42 at a rate of approximately 1.0 m/s, the components comprisingthe inertia valve 138 will preferably be configured such that virtuallyall of the hydraulic fluid flows into the reservoir chamber 128 via thereservoir shaft fluid ports 148 and, accordingly, such that only a smallvolume of hydraulic fluid flows through the compression flow passages174 at that rate of piston 68 movement. However, the inertia valve 138of that same embodiment will preferably be configured such that, whenthe rear shock 38 encounters a more severe bump that causes the piston68 to move within the hydraulic fluid body portion 42 at a rate ofapproximately 4.0 m/s, the components comprising the inertia valve 138will preferably be configured such that approximately 20% or more of thetotal flow of hydraulic fluid flowing into the reservoir chamber 128will flow through the reservoir shaft fluid ports 148 and approximately80% or less of the total flow of hydraulic fluid flowing into thereservoir chamber 128 will flow through the compression flow passages174.

In certain embodiments, when the rear shock 38 encounters a more severebump that causes the piston 68 to move at a rate of approximately 4.0m/s, the components comprising the inertia valve 138 will preferably beconfigured such that at least 80%, at least 70%, at least 60%, at least50%, at least 40%, or at least 35% of the total flow of hydraulic fluidflowing into the reservoir chamber 128 will flow through passages otherthan passages closable by the inertia mass 150 (in the illustratedembodiment, the compression flow passages 174 and the bleed valve port171).

In certain embodiments, the inertia valve 138 will preferably beconfigured such that, when the rear shock 38 encounters a more severebump that causes the piston 68 to move at a rate of approximately 4.0m/s, the components comprising the inertia valve 138 will preferably beconfigured such that no more than 10%, no more than 20%, no more than30%, no more than 40%, no more than 50% or no more than 60% of the totalflow of hydraulic fluid flowing into the reservoir chamber 128 will flowthrough the passages closable by the inertia mass (in the illustratedembodiment, the reservoir shaft fluid ports 148).

The inertia mass 150 is preferably made from brass and preferably has amass less than approximately two ounces. In another embodiment, theinertia mass 150 preferably has a mass less than approximately one andone-half ounces. In another embodiment, the inertia mass 150 has aweight of approximately 32 grams, or 1.13 ounces. In another embodiment,the inertia mass 150 preferably has a mass less than approximately oneounce. In yet another embodiment, the inertia mass 150 preferably has amass less than or equal to approximately one-half ounce. The inertiamass 150 preferably is free of any axial passages or other sophisticatedinternal features or contours other than the main, cylindrical passagethrough the longitudinal center of the inertia mass 150, and also theannular groove 151 on the inside surface of the inertia mass 150.Without such passages and sophisticated internal features and contours,the inertia mass 150 is advantageously easier to manufacture, does notrequire substantial deburring on the internal surfaces, and is lesslikely to bind or stick to the reservoir shaft 134 as compared to other,conventional designs. Preferably, the inertia mass 150 has a streamlinedgeometric configuration such that the mass to fluid resistance ratio isincreased. The annular groove 151 is preferably formed on the insidesurface of the inertia mass 150 to limit the amount of surface area onthe inside surface of the inertia mass 150 that may come into contactwith the outer surface of the reservoir shaft 134 and, hence, limit theamount of drag between the two components. The inertia mass 150 may alsohave an annular groove 153 around the exterior of the inertia mass 150.

As mentioned above, the spring 152 biases the inertia mass 150 into anupward, or closed, position wherein the inertia mass 150 covers theopenings of the reservoir shaft fluid ports 148 to substantially preventfluid flow from the passage 136 to the reservoir chamber 128.Preferably, when the inertia mass 150 is in a closed (upward) position,flow to the reservoir chamber 128 primarily occurs through thecompression flow passages 174 in the cap 160. FIG. 13 illustrates theflow of hydraulic fluid from the passage 136 through the compressionflow passages 174 in the cap 160 and into the reservoir chamber 128, aswell as the corresponding preferred deflection of the compression flowshim stack 178, when the inertia valve 138 is in the closed position.However, the flow path, but not necessarily the flow volume, ofhydraulic fluid through the compression flow passages 174 in the cap 160and into the reservoir chamber 128 may be as illustrated in FIG. 13 evenif the inertia valve 138 were in an open position.

The inertia mass 150 is also movable into a downward, or open, positionagainst the biasing force of the spring 152. In the open position, whichis illustrated in FIGS. 15 and 16, the inertia mass 150 uncovers atleast some of the reservoir shaft fluid ports 148 to allow fluid to flowtherethrough, and a reduced compression damping rate is achieved. Asillustrated in FIG. 10, the end cap 132 preferably operates as thelowermost stop surface for the inertia mass 150. FIG. 16 illustrates theflow of hydraulic fluid through the inertia valve 138 during thecompression motion of the rear shock 38 while the inertia mass 150 is inthe open position. In this configuration, hydraulic fluid flows from thepassage 136 through the reservoir shaft fluid ports 148, around the base158 and cap 160 and into the reservoir chamber 128. Note that, while theinertia mass 150 is in the open position, hydraulic fluid may still flowfrom the passage 136 through the compression flow passages 174 in thecap 160 and into the reservoir chamber 128, as illustrated in FIG. 13,in addition to flowing through inertia valve.

It is noted that, while the inertia mass 150 may be described as havingan open and a closed position, the inertia mass 150 likely does notcompletely prevent flow through the reservoir shaft fluid ports 148 inthe closed position. That is, a fluid-tight seal is not typicallycreated between the inertia mass 150 and the reservoir shaft 134 onwhich it slides. Thus, some fluid may flow through the inertia valve 138in its closed position. Such fluid flow is often referred to as “bleedflow” and, preferably, is limited to a relatively small flow rate. Tocreate a fluid-tight seal between the inertia mass 150 and the reservoirshaft 134 would require precise dimensional tolerances, which would beexpensive to manufacture, and may also inhibit movement of the inertiamass 150 on the reservoir shaft 134 in response to relatively smallacceleration forces.

With reference to FIGS. 12-16, another advantageous feature of theillustrated inertia valve 138 is a circumferential groove 188 around theexterior of the reservoir shaft 134. The center plane of the groove 188preferably aligns with the axial centerlines of each of the reservoirshaft fluid ports 148. The groove 188 functions as a flow accumulator,equalizing the pressure of the hydraulic fluid emanating from thereservoir shaft fluid ports 148.

As most clearly illustrated in FIG. 16, the groove 188 preferablycomprises an upper chamfer portion 188 a, an arcuate portion 188 b, anda lower chamfer portion 188 c. The width of the groove 188 (i.e., thecombined width of the upper chamfer portion 188 a, the arcuate portion188 b, and the lower chamfer portion 188 c) is preferably greater thanthe diameter of each of the reservoir shaft fluid ports 148 such thegroove 188 extends both above and below each of the reservoir shaftfluid ports 148 and such that a significant amount of fluid canaccumulate in the groove 188. In another embodiment, the groove 188could be smaller than the diameter of the ports 148. The groove 188allows the fluid pressure to be distributed evenly over the innercircumference of the inertia mass 150. The even distribution of fluidpressure preferably creates a force tending to center the inertia mass150 around the reservoir shaft 134, thus partially or fully compensatingfor any inconsistencies in fluid pressure that would otherwise occur dueto the locations or orientations of, or variations in size between, thereservoir shaft fluid ports 148. Such a feature helps to prevent bindingof the inertia mass 150 on the reservoir shaft 134. The prevention ofbinding of the inertia mass 150 on the reservoir shaft 134 is beneficialin a bicycle application because it is desirable that the inertia valvebe very sensitive to any terrain features which may only transmitrelatively small acceleration forces to the inertia valve 138.

The preferred configuration of the groove 188 illustrated in FIG. 16provides a nearly uniform (i.e., simultaneous) cutoff of hydraulic fluidflow emanating from each of the reservoir shaft fluid ports 148 as theinertia mass 150 reverts to its closed position. This is beneficial toensuring that the inertia mass is not pushed off-center by the reservoirshaft fluid ports 148. As discussed, the preferred configuration of thegroove 188 also advantageously ensures that the inertia mass 150 is notpushed off-center by a non-uniform flow of hydraulic fluid through thereservoir shaft fluid ports 148, or by non-uniform forces exerted by thehydraulic fluid flowing through the reservoir shaft fluid ports 148,during the compression motion of the rear shock 38.

Additionally, the chamfers 188 a advantageously provide for aprogressive shut off of hydraulic fluid flow through the reservoir shaftfluid ports 148 as the inertia mass 150 reverts to its closed position.In particular, as the acceleration causing the inertia mass 150 to movedownward relative to the reservoir shaft fluid ports 148 is reduced,causing the inertia mass 150 to move upward, the inertia mass 150 firstblocks the flow of hydraulic fluid flowing away from the lower chamferportion 188 c, thus blocking only a portion of the hydraulic fluid flowgoing through the reservoir shaft fluid ports 148 in this position. Thehydraulic fluid flowing from the lowest portion of the lower chamferportion 188 c is less than the hydraulic fluid flowing from the upperportion of the lower chamfer portion 188 c. Thus, as the hydraulic mass150 continues to move upward, it progressively blocks a greater amountof the hydraulic fluid flowing away from the lower chamfer portion 188c. As the hydraulic mass 150 continues to move upward, it progressivelyblocks a greater portion of the arcuate portion 188 b and, finally, theupper chamfer portion 188 a, until substantially all of the hydraulicfluid flowing through the reservoir shaft fluid ports 148 is stopped.

Although the illustrated reservoir body portion 44 includes an inertiavalve 138, in other arrangements, the inertia valve 138 may be omittedor may be replaced with, or supplemented with, other compression orrebound fluid flow valves. However, the inertia valve 138 is preferredbecause it operates to distinguish terrain-induced forces fromrider-induced forces. Terrain-induced forces are generally upwardlydirected (compression) forces caused by the vehicle (such as a bicycle)encountering a bump. Rider-induced forces, in the case of a bicycleapplication, typically are short duration, relatively large amplitudeforces generated from the pedaling action of the rider. The inertiavalve may alternatively be configured to operate in response to reboundforces, rather than compression forces.

The operation of the rear shock 38 is now discussed in detail, withreference to FIGS. 1-16. As discussed above, the rear shock 38 ispreferably mounted between the seat post tube 25 and the subframeportion 26 of the bicycle 20. Preferably, the hydraulic fluid bodyportion 42 portion of the rear shock 38 is connected to the subframeportion 26 and the air tube 40 is connected to the seat post tube 25. Asshown in FIG. 1, the reservoir body portion 44 is preferably connectedto the subframe portion 26 of the bicycle 20 near the rear axle. Therear shock 38 is capable of both compression and rebound motion.

When the rear wheel 30 of the bicycle 20 is impacted by a bump, thesubframe portion 26 rotates with respect to the main frame portion 24,tending to compress the rear shock 38. The inertia mass 150 is biased bythe force of the spring 152 to remain in the closed position. The closedposition of the inertia valve 138 is illustrated in FIGS. 10, and 12-14.In order for the inertia mass 150 to overcome the force of the spring152 and move to an open position such that fluid flows from the passage136 through the reservoir shaft fluid ports 148 and into the reservoirchamber 128, the inertia mass 150 must be in an open position. The openposition of the inertia mass 150 is shown in FIGS. 15 and 16. Theinertia mass 150 translates to the open position if the accelerationexperienced by the reservoir body portion 44 along its longitudinal axisexceeds a predetermined threshold value.

For compression motion of the rear shock 38 (i.e., for the piston member68 to move into the hydraulic fluid body portion 42), the fluid that isdisplaced from the shock shaft 70 must flow into the reservoir chamber128. However, when the inertia mass 150 is in a closed position withrespect to the reservoir shaft fluid ports 148, fluid flow into thereservoir chamber 128 is preferably substantially impeded. When theinertia valve 138 is in the closed position, the rear shock 38preferably remains substantially rigid.

However, even if the inertia valve 138 remains in the closed position,fluid can still transfer from the compression chamber 96 into thereservoir chamber 128 if the compressive force exerted on the rear shock38 is of a magnitude sufficient to increase the fluid pressure withinthe primary valve chamber 170 to an amount that will cause thecompression flow shim stack 178 to open and allow fluid to flow from theprimary valve chamber 170 through the compression flow passages 174 andinto the reservoir chamber 128.

In the configurations described herein, the spring force of the rearshock 38 is produced by the pressure of the gas in the primary airchamber 86. The damping rate in compression is determined mainly by theflow through the compression flow passages 174 in the reservoir bodyportion 44, as well as the less significant damping effects produced bythe compression shim stack 106 in the main body portion 39.

If a sufficient magnitude of acceleration is imposed along thelongitudinal axis of the reservoir body portion 44 (i.e., the axis oftravel of the inertia mass 150), the inertia mass 150 will overcome thebiasing force of the spring 152 and move downward relative to thereservoir shaft 134 into an open position. The open position of theinertia mass is illustrated in FIGS. 15 and 16. With the inertia valve138 in the open position, hydraulic fluid is able to be displaced fromthe compression chamber 96 through the passages 112, 114 and the shaftpassage 136, through the reservoir shaft fluid ports 148 and into thereservoir chamber 128. Thus, the rear shock 38 is able to be compressedand the compression damping is preferably determined primarily by flowthrough the compression flow passages 174 in the reservoir body portion44 as well as the reservoir shaft fluid ports 148.

The mass of the inertia mass 150, the spring rate of the spring 152, andthe preload on the spring 152 determine the minimum threshold for theinertia mass 150 to overcome the biasing force of the spring 152 andmove to the open position. The spring rate of the spring 152 and thepreload on the spring 152 are preferably selected such that the inertiamass 150 is biased by the spring 152 into a closed position when noupward acceleration is imparted in the axial direction of the reservoirbody portion 44. However, the inertia mass 150 will preferably overcomethe biasing force of the spring 152 when subject to an acceleration thatis between 0.1 and 3 times the force of gravity (G's). Preferably, theinertia mass 150 will overcome the biasing force of the spring 152 uponexperiencing an acceleration that is between 0.25 and 1.5 G's. However,the predetermined threshold may be varied from the values recited above.

With reference to FIGS. 15 and 16, when the inertia mass 150 is in theopen position, the spring 152 exerts a biasing force on the inertia mass150 which tends to move the inertia mass 150 toward the closed position.Advantageously, with the exception of the spring biasing force and fluidresistance, the inertia mass 150 moves freely within the body of fluidcontained in the reservoir chamber 128 to increase the responsiveness ofthe inertia valve 138 and, hence, the rear shock 38 to forces exerted onthe rear wheel 30. The inertia valve 138 differentiates between bumpysurface conditions and smooth surface conditions, and alters the dampingrate accordingly. During smooth surface conditions, the inertia valve138 remains in a closed position and the damping rate is desirably firm,thereby inhibiting suspension motion due to the movement of the rider ofthe bicycle 20. When the first significant bump is encountered, theinertia valve 138 opens to advantageously lower the damping rate so thatthe bump may be absorbed by the rear shock 38.

Once the rear shock 38 has been compressed, either by fluid flow throughthe primary valve assembly 140 or the inertia valve 138, the springforce generated by the combination of the primary air chamber 86 and thesecond air chamber 88 tend to bias the hydraulic fluid body portion 42away from the air tube 40. In order for the rear shock 38 to rebound, avolume of fluid equal to the displaced volume of the shock shaft 70 mustbe drawn from the reservoir chamber 128 and into the compression chamber96. Fluid flow is allowed in this direction through the refill ports 176in the primary valve assembly 140 against a desirably light resistanceoffered by the rebound flow shim stack 180. Gas pressure within the gaschamber 130 exerting a force on the floating reservoir piston 124 mayassist in this refill flow. Thus, the rebound damping rate is determinedprimarily by fluid flow through the rebound flow passages 108 againstthe biasing force of the rebound shim stack 110.

As discussed, the present rear shock 38 includes an inertia valve 138comprising an inertia mass 150 and a reservoir shaft 134 having acircumferential groove 188 in the reservoir shaft 134 aligned with thereservoir shaft fluid ports 148 to create an even distribution of fluidpressure on the inertia mass 150 and, hence, prevent the inertia mass150 from binding on the reservoir shaft 134. The off-center condition ofthe inertia mass 150 may cause it to contact the reservoir shaft 134causing friction, which tends to impede motion of the inertia mass 150on the reservoir shaft 134. Due to the relatively small mass of theinertia mass 150 and the desirability of having the inertia mass 150respond to small accelerations, any friction between the inertia mass150 and the reservoir shaft 134 seriously impairs the performance of theinertia valve 138 and may render it entirely inoperable. The off-centercondition may result from typical errors associated with themanufacturing processes needed to produce the components of the inertiavalve 138. Further, the binding effect of the inertia mass 150 mayresult from burrs located on the inner surface of the inertia mass 150or the outer surface of the reservoir shaft 134. Because the inertiamass 150 advantageously has a generally smooth inner surface, thedeburring operations on the inside surface of the inertia mass 150 aresubstantially simplified and the risk of binding is substantiallyreduced.

As the accompanying figures show, the rear shock 38 has other featuresand components such as seals which will are shown but not describedherein that are obvious to one of ordinary skill in the art.Accordingly, a discussion of these features has been omitted.

Although the present invention has been explained in the context ofseveral preferred embodiments, minor modifications and rearrangements ofthe illustrated embodiments may be made without departing from the scopeof the invention. For example, but without limitation, although thepreferred embodiments described the bicycle damper for altering the rateof compression damping, the principles taught may also be utilized indamper embodiments for altering rebound damping, or for responding tolateral acceleration forces, rather than vertical acceleration forces.In addition, although the preferred embodiments were described in thecontext of an off-road bicycle application, the present damper may bemodified for use in a variety of vehicles, or in non-vehicularapplications where dampers may be utilized. Furthermore, the pressureand flow equalization features of the inertia valve components may beapplied to other types of valves, which may be actuated by accelerationforces or by means other than acceleration forces. Accordingly, thescope of the present invention is to be defined only by the appendedclaims.

1. (canceled)
 2. A method of damping motion using a damper coupled to abicycle frame, the damper comprising a primary unit and a reservoirtube, the reservoir tube positioned outside of a damper tube of theprimary unit, the damper tube and reservoir tube fluidly coupled by aflow path, the method comprising: providing a damping fluid within acompression chamber of the damper tube, the compression chamber definedat least partially by a wall of the damper tube and a main pistonmovably positioned within the damper tube; resisting, by the dampingfluid, movement of the main piston within the damper tube in a directionthat reduces a size of the compression chamber; selectively reducing theresistance to movement of the main piston by one or both of thefollowing: opening, responsive to a terrain-induced force, an inertiavalve within the reservoir tube, the opening of the inertia valveallowing at least some fluid to flow from the compression chamber of thedamper tube into a reservoir chamber of the reservoir tube through theinertia valve; and allowing, responsive to a 50 pounds or greater forcebeing applied to a damping valve within the reservoir tube, at leastsome fluid to flow from the compression chamber of the damper tube intothe reservoir chamber of the reservoir tube through the damping valve.3. The method of claim 2, wherein the selectively reducing theresistance to movement of the main piston further comprises: opening thedamping valve before flow through the inertia valve reaches an absolutemaximum amount of flow capable of passing through the inertia valve. 4.The method of claim 2, further comprising: compressing, by fluid flowinginto the reservoir chamber, a spring chamber of the reservoir tube; andexpanding the spring chamber of the reservoir tube when the main pistonmoves in a direction that increases the size of the compression chamber.5. The method of claim 2, further comprising: compressing a springchamber of the primary unit when the main piston moves in the directionthat reduces the size of the compression chamber.
 6. The method of claim2, further comprising: maintaining the inertia valve in a closedposition, except in response to terrain-induced forces, wherein theinertia valve comprises increased resistance to fluid flow therethroughin the closed position than in an open position.
 7. The method of claim6, wherein the allowing at least some fluid to flow through the dampingvalve further comprises: damping, with the damping valve, at a firstdamping rate when the inertia valve is in the open position; anddamping, with the damping valve, at a second damping rate when theinertia valve is in the closed position, wherein the second damping rateis stiffer than the first damping rate.
 8. The method of claim 2,wherein the allowing at least some fluid to flow through the dampingvalve further comprises: deflecting a shim stack away from one or moreports of a damping valve piston.
 9. The method of claim 2, wherein theallowing at least some fluid to flow through the inertia valve furthercomprises: allowing fluid to flow through a plurality of inertia valveflow passages having a total cross-sectional area of not more than 8millimeters squared.
 10. The method of claim 2, wherein the allowing atleast some fluid to flow through the inertia valve further comprises:allowing fluid to flow through a plurality of inertia valve flowpassages having a total cross-sectional area of not more than 6millimeters squared.
 11. The method of claim 2, wherein at a main pistonspeed of 4 meters/second at least 50% of compression damping in thereservoir tube occurs in a circuit which is not closable by the inertiavalve.
 12. A method of damping motion using a damper coupled to abicycle frame, the damper comprising a primary unit and a reservoirtube, the reservoir tube positioned outside of a damper tube of theprimary unit, the damper tube and reservoir tube fluidly coupled by aflow path, the method comprising: providing a damping fluid within acompression chamber of the damper tube, the compression chamber definedat least partially by a wall of the damper tube and a main pistonmovably positioned within the damper tube; resisting, by the dampingfluid, movement of the main piston within the damper tube in a directionthat reduces a size of the compression chamber; opening, responsive to aterrain-induced force, an inertia valve within the reservoir tube,wherein the opening of the inertia valve reduces the resistance tomovement of the main piston by allowing at least some fluid to flow fromthe compression chamber of the damper tube into a reservoir chamber ofthe reservoir tube through the inertia valve; opening a damping valvewithin the reservoir tube, responsive to a 50 pounds or greater forcebeing applied to the damping valve, wherein the opening of the dampingvalve reduces the resistance to movement of the main piston by allowingat least some fluid to flow from the compression chamber of the dampertube into the reservoir chamber of the reservoir tube through thedamping valve.
 13. The method of claim 12, wherein the opening of thedamping valve occurs before flow through the inertia valve reaches anabsolute maximum amount of flow capable of passing through the inertiavalve.
 14. The method of claim 12, further comprising: compressing, byfluid flowing into the reservoir chamber, a spring chamber of thereservoir tube; and expanding the spring chamber of the reservoir tubewhen the main piston moves in a direction that increases the size of thecompression chamber.
 15. The method of claim 12, further comprising:compressing a spring chamber of the primary unit when the main pistonmoves in the direction that reduces the size of the compression chamber.16. The method of claim 12, further comprising: maintaining the inertiavalve in a closed position, except in response to terrain-inducedforces, wherein the inertia valve comprises increased resistance tofluid flow therethrough in the closed position than in an open position.17. The method of claim 16, wherein the allowing at least some fluid toflow through the damping valve further comprises: damping, with thedamping valve, at a first damping rate when the inertia valve is in theopen position; and damping, with the damping valve, at a second dampingrate when the inertia valve is in the closed position, wherein thesecond damping rate is stiffer than the first damping rate.
 18. Themethod of claim 12, wherein the allowing at least some fluid to flowthrough the damping valve further comprises: deflecting a shim stackaway from one or more ports of a damping valve piston.
 19. The method ofclaim 12, wherein the allowing at least some fluid to flow through theinertia valve further comprises: allowing fluid to flow through aplurality of inertia valve flow passages having a total cross-sectionalarea of not more than 8 millimeters squared.
 20. The method of claim 12,wherein the allowing at least some fluid to flow through the inertiavalve further comprises: allowing fluid to flow through a plurality ofinertia valve flow passages having a total cross-sectional area of notmore than 6 millimeters squared.
 21. The method of claim 12, wherein ata main piston speed of 4 meters/second at least 50% of compressiondamping in the reservoir tube occurs in a circuit which is not closableby the inertia valve.